The eye contains a natural crystalline lens which is supported by a capsular bag or sac located behind the pupil and iris. Light is received through the cornea and pupil, and focused by the lens in a sharp image on the retina to provide vision.
Loss of vision can result when the natural lens becomes clouded or opaque, a condition known as a cataract. To prevent blindness, the accepted medical procedure calls for surgical removal of the natural lens from the eyeball followed by adaptation of an artificial lens to correct vision. Absence of the natural lens from the eye is known as aphakia. The optical correction of this condition is called aphakia correction.
There are several approaches to vision restoration or correction. One method entails fitting the patient with glasses. However, glasses reduce peripheral vision, magnify the objects viewed, and are feasible only when cataracts are removed from both eyes because double vision results if glasses are used after cataract removal from a single eye. Glasses, however, are not generally suitable for treatment of cataracts due to the extent of correction required and distortion resulting therefrom.
In another method, a contact lens is worn on the eye to achieve better peripheral vision at a lower magnification factor than glasses. Unfortunately, many cataract patients are relatively advanced in age and have difficulty in adjusting to contact lenses and in manipulating them for insertion, and therefore cannot wear contact lenses.
Yet another more recently developed method of vision correction involves the implantation of an artificial lens within the eye. This is accomplished by a delicate and precise surgical procedure, and there have been various approaches to such devices. Intraocular lens devices, of course, must be accurately designed and implanted for successfully restoring vision while minimizing irritation of sensitive eye structure and postoperative complications. It will be apparent that minute changes in the design and implantation technique of such lenses can be determinative of success or failure.
Intraocular lenses have been developed for placement in the anterior chamber as well as in the posterior chamber. After unsuccessful attempts by Harold Ridley and others to develop lenses for placement in the posterior chamber, efforts turned to development of anterior chamber devices. Fixation and centration, however, are problems common to both types of lenses.
Intraocular lenses must be implanted and stabilized in a way which is resistant to dislocation, but which accommodates the involuntarily movement of the iris. In order to minimize these problems, several types of iris-clip and iridocapsular lenses have come about. For example, a lens known as the Binkhorst iris-clip lens uses nylon loops which are sutured to the iris. Suturing is undesirable because special techniques are required in their installation, in addition to the fact that sutures may tear loose from the iris and eventually dissolve to cause dislocation of the lens. Other intraocular lens designs employ one or more loops in combination with one or more pins to attach the lens to the iris. Single pin lenses of the prior art, however, have tended to become dislocated in some cases.
Although anterior chamber lenses have been more popular, there are cases in which posterior chamber lenses are preferred by some surgeons. For example, a posterior chamber lens may be preferable in cases of traumatic cataract requiring extracapsular extraction of the natural lens. However, the lack of a scleral spur in the posterior chamber, which is the natural location, poses a special problem in that the lens must be placed in the more sensitive ciliary body.
Difficulties with previous posterior chamber lenses included nonfixation, poor centration and other complications. One prior design effects centration by the spring action of opposed resilient legs engaged with the ciliary body, the long term effect of which is unknown but potentially detrimental. In another posterior chamber design of the prior art, centration is effected by a suture between the upper haptic thereof and the iris. Dilation of the pupil can cause dislocation of this lens design. Another design employs a plurality of prongs or pins clipped to the iris about the pupil.
There is thus a need for an improved intraocular lens for encapsulation in the posterior chamber which allows movement of the iris relative thereto with increased stability against dislocation and thus decentration of the lens.